Recent evidence suggests that child day care attendance may increase the risk of developing primary Haemophilus influenzae type b (Hib) disease by more than ten-fold over than for children not attending day care. Data also indicate that the risk of disease for day care contacts of a case is increased but that many of the subsequent cases occur more than sixty days after exposure to the primary case. However, only limited information is available to determine whether or not the isolates from the "late onset" cases are the same as those from the respective primary cases. To evaluate the impact of child day care attendance on the epidemiology of Hib disease, active population-based surveillance of Hib disease will be carried out concurrently in Dallas County, Texas and the State of Minnesota. Preliminary data indicate that day care facilities, day care practices, and the epidemiology of Hib disease differ significantly in these regions. 1) A case-control study will be conducted to determine the relative risk of primary Hib disease among children in day care in these regions. 2) A study comparing day care facilities with and without Hib cases will be performed to determine if certain day care practices are risk factors. 3) The incidence of Hib disease in day care contacts of a case will be determined and; 4) Studies of Hib colonization and acquisition will be conducted to determine the patterns of transmission of Hib after exposure of a day care contact to a primary case. Finally, 5) we intend to characterize the Hib isolates by multiple molecular strain markers, including outer membrane protein PAGE profiles, isoenzyme (allozyme) electrophoretic typing, and reactivity with monoclonal antibodies. These laboratory studies will permit us to subclassify Hib isolated into multiple groups, thereby providing a powerful tool for epidemiologic analysis. Characterization of Hib strains isolated from patients also will permit us to determine if certain Hib strains (clonotypes) have a greater propensity to colonize and/or cause invasive disease than others. The proposed studies will provide a unique opportunity to investigate patterns of transmission of a model respiratory bacterial pathogen in a day care setting. Defining potentially preventable factors which affect the occurrence of Hib disease will allow development of more rational guidelines for prevention of this, and possibly, other bacterial diseases in day care.